Sjgren's syndrome encompasses a disease spectrum with significant heterogeneity. Accumulating data indicates that this heterogeneity reflects the predominance of different disease mechanisms in different patient subsets. Defining relevant mechanistic markers is essential for accurate diagnosis, identification of disease subsets, monitoring of disease activity and prediction of outcome, and potentially for selection of therapy in Sjgren's syndrome. While high-titer autoantibodies are a frequent feature in Sjgren's syndrome, they are not always detected, despite universal lymphocytic infiltration of salivary glands. Our preliminary data shows that there are additional Sjgren's autoantigens recognized by sera from apparently seronegative patients - these antigens are not expressed in cells used as standard antigen sources for autoantibody detection. We propose that different amplifying pathways (e.g. IFNs, cellular cytotoxicity, tissue repair and regeneration) are associated with distinct antigen expression fingerprints, and generation of novel autoantibodies. Furthermore, we propose that definition of additional new autoantibodies reflecting these pathways will provide additional tools for patient classification based on mechanisms active in their tissues. The long term goals of this program are to define novel autoantibodies and autoantigens as probes of mechanisms in Sjgren's syndrome. We will pursue the following specific aims: (i) Define and identify new autoantibodies targeting inducible and developmental autoantigens using SS sera to screen IFN-treated cells and immature epithelial cells as novel autoantigen sources, and demonstrate that B cells with these specificities can be found in the salivary gland of patients with SS; (ii) Define the associations of autoantibodies recognizing inducible and developmental autoantigens with distinct SS phenotypes, and specific autoantigen expression in the SS target tissue; (iii) Demonstrate that the components of a sustaining pathogenic loop interact directly in SS salivary glands by showing enhanced autoantigen expression, together with cytotoxic lymphocyte-specific proteolysis of the same autoantigens recognized by infiltrating T cells in those glands. Since it is likely that distinct disease mechanisms predominate in different patient subsets, phenotype-specific autoantibodies and autoantigen expression in the target tissue constitute tools for molecular subsetting - quantitatively or semi-quantitatively assessing specific pathways in vivo - and may facilitate diagnosis, classification and therefore more targeted therapy in this complex, heterogeneous disease process.